A common metal binding motif, namely the 2-His-l-carboxylate (2H-1D/E) facial triad, is emerging in metalloenzymes that catalyze dioxygen activation. These enzymes catalyze a diverse range of "metabolically important transformations. The reduction-oxidation (redox) potentials of these 2H-1D/E dependent metal centers are proposed to play an important role in this dioxygen activation, and it is the goal of this proposal to better understand this role. Specifically, this study aims to characterize the redox potential between the resting M2+ and the oxidized M3+ states of metalloenzymes with the 2H-1D/E metal binding motif. This study will provide a benchmark to compare metal centers within this family of enzymes, thus beginning a collection of physical properties describing the 2H-1D/E metal binding motif. To do this, we propose to characterize the chemically oxidized 2H-1D/E dependent metal centers both spectroscopically and chemically. Probing these centers with a series of dioxygen related species, we will explore the chemistry of these active centers, explicitly searching for intermediates similar to those proposed in their reaction mechanisms.